Local food is usually more "green" than organic food, according to a report published in the journal Food Policy.

The authors say organic farming is also valuable, but people can help the environment even more by buying food from within a 20km (12-mile) radius.

The team calculated a shopping basket's hidden costs, which mount up as produce is transported over big distances. The study found "road miles" account for proportionately more environmental damage than "air miles".

Therefore, the researchers' message to consumers is this: it is not good enough to buy food from within the UK - it is better if it comes from within your area, too.

A big city like London could be provided with a lot more seasonal vegetables from local farms

Co-author Professor Tim Lang

However, they admit that consumers are prevented from "doing the right thing" because of inadequate labelling.

"The most political act we do on a daily basis is to eat, as our actions affect farms, landscapes and food businesses," said co-author Professor Jules Pretty, from the University of Essex, UK.

"Food miles are more significant than we previously thought, and much now needs to be done to encourage local production and consumption of food."

Clean-up costs

Professor Pretty and his colleague Tim Lang, from City University, UK, painstakingly estimated the environmental price tag on each stage of the food production process.

That price might reflect, for example, the clean-up costs following pollution, or the loss of profits caused by erosion damage.

The price of food is disguising externalised costs

"The price of food is disguising externalised costs - damage to the environment, damage to climate, damage to infrastructure and the cost of transporting food on roads," Professor Lang told the BBC News website.

The authors calculated that if all foods were sourced from within 20km of where they were consumed, environmental and congestion costs would fall from more than £2.3bn to under £230m - an "environmental saving" of £2.1bn annually.

They pointed out that organic methods can also make an important contribution. If all farms in the UK were to turn organic, then the country would save £1.1bn of environmental costs each year.

Consumers can save a further £100m in environmental costs, the authors claim, if they cycle, walk or catch the bus to the shops rather than drive.

Each week, the average person clocks up 93p worth of environmental costs, the report concludes.

These costs should be addressed by the government, companies and consumers, the authors believe.

Sophisticated policy

"It is going to need some sophisticated policy solutions," Professor Pretty said. "You could say we should internalise those costs in prices, so that it affects people's behaviour. That might be economically efficient but it lacks on the social justice side because it will affect rich people much less."

Instead, the authors are advocating a softer approach. Consumers should make ethical choices about the food that they buy, and supermarkets should be open with customers about where their food is coming from.

At the moment, as every UK consumer will know, it is impossible to tell whether your carrot has come from Devon or Scotland.

At the moment it is impossible to tell whether your carrot has come from Devon or Scotland

"In the short term, our paper adds to consumer frustration," Professor Lang concedes. "The problem is we don't get the information. Food labels don't tell you the sort of information you really need to know if you want to do the right thing by the environment."

Since supermarkets do know exactly where their food is coming from, Professor Lang believes they have a duty to inform their customers.

Eventually, the authors hope, the food production infrastructure within Britain will be transformed.

"We think farming methods will change - farming will undergo a re-birth, if you like," said Professor Lang.

"A big city like London could be provided with a lot more seasonal vegetables from local farms - because at the moment, the shape of the supply chain is all wrong from the point of view of food, environment and public health."

Your comments

My Welsh/Canadian grandfather grew most of our food and it tasted wonderful. Store-bought food lacks the flavours of fresh. One day I watched asparagus being harvested about 20 miles from my home. The cut spears lay on a tarp, under the hot sun for almost an hour before being placed on a truck and hauled off to market. Even locally grown food may be poorly handled. So like my grandfather, I try to grow as much at home that I can. I agree with the gentleman from San Diego. Americans have much to relearn about food.A Davis, Anaheim USA

The article states: "At the moment, as every UK consumer will know, it is impossible to tell whether your carrot has come from Devon or Scotland." but even if we did know, this isn't the whole story. Food is moved from British suppliers to centralised supermarket depots, then back to the branches, so even if something appears to be local, then it may in fact have travelled up and down the country to reach you. There's a whole section on this in Felicity Lawrence's excellent book "Not on the label". The only real way to ensure you're eating local food is use farmers' markets and local shops, or grow it yourself! I think we should be lobbying the supermarkets hard on this issue.Margot Maynard, London, UK

I know of just two "farmer's markets" available in Riverside - one only part of the year; even those have produce from further away than 12 miles. I usually shop at a supermarket where the majority of the fresh food is grown in Southern CA [at least]. I know of no way to ensure that the foods I eat are grown within 12 miles of my home - short of raising some veggies myself. I would like to, however it is not possible as it would be too time consuming.J P, Riverside, CA USA

Apart from the road miles, food grown locally is most suitable for the people living in that climate

Meena Appnender, Hyderabad, India

I agree. Apart from the road miles, food grown locally is most suitable for the people living in that climate. It is likely that all the nutrients are likely to be found in various forms in the locally grown produce.Meena Appnender, Hyderabad, India

"The most political act we do on a daily basis is to eat". I couldn't agree more. The country I live in may be democratic, but above all, it is capitalist. The only real power we have these days is the power of the penny... each cent spent is a clear vote to change or maintain the status quo. The only way to change our markets is to support those products that attempt to be environmentally sound and humane to animals. Thanks for running this piece, I only wish the media in my country would follow suit.Owen, San Diego, USA

I have always thought that the definition of organic should include food miles. There is not a lot of point in eating good food if there is a greater impact on the planet by getting it on your plate. How we suffer from narrow definitions. We need a more holistic view of all the issues in food quality and production/transport. Keep up the good work.Maurice Hopper, Exeter

We need to re-educate ourselves to eat seasonally, and to encourage local producers

Caroline Deamer, Lincoln, UK

I agree wholeheartedly, and it's heartening to have this 'instinct' confirmed through scientific analysis. We need to re-educate ourselves to eat seasonally, and to encourage local producers. However, there are seemingly some disincentives for doing this, in the economic model currently adopted, with supermarkets dominating the food supply chain. Hopefully (although this is a somewhat vain hope) consumers and the government might actually take notice now that there is a financial perspective on this...but I doubt itCaroline Deamer, Lincoln, UK

This idea seems a little ridiculous, what if there are no farms within 12 miles of your house, and am I supposed to live on Rhubarb as this is the main thing grown locally to me!Paul Hartshorne, Leeds

Yes, I agree very much. Progress has taken us away from some very good "habits", how does "progress" take us back? Thanks for the article.Cyd Hanns, Barrow, Alaska

I would love to see a follow up article about how existing homes could be retrofitted with a relatively low cost solarium/greenhouse that could help to passively solar heat the home while producing vegetables, herbs etc year round. This could be used by people who were already planning to renovate their home. Of course it would be much easier to accomplish this in new construction of homes and even large buildings with flats. Homeowners, like farmers, should be given the economic incentive/reward for making their homes more environmentally friendly! The trend to working at home should also be rewarded as it cuts down on traffic on the road, reduces pollution, and has other positive benefits. I think your scheme in the UK to reward farmers for making their lands more wildlife friendly is "brilliant" as you might say!Tom Lang, Lions Bay, Canada